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Improved understanding of the cryosphere's response to climate variability is essential for accurate sea-level rise estimates in light of projected 21st century warming. Recently, the overall mass of the Greenland Ice Sheet has decreased, driven in part by acceleration of ice streams and outlet glaciers located on the ice sheet periphery. However, acceleration and short-term fluctuations of these ice masses has made predicting the rate and regional variability of future ice sheet retreat extremely difficult. Furthermore, modern observations of ice sheet change lack a historical context against which these changes can be evaluated. Doctoral student Nicolás Young at the State University of New York Buffalo, under the supervision of Dr. Jason Briner will reconstruct past fluctuations of Jakobshavn Isbræ, Greenland's largest and most active ice stream, and determine the driving mechanisms behind these changes. Specifically, this research will explore if ice margin advance and retreat between 10,000 and 8,000 years ago was climate-driven, or if ice margin position was mainly controlled by non-climatic factors. Of particular interest is gauging whether regional, centennial-scale cold perturbations occurring between 9,200 and 8,200 years ago triggered an advance of the ice sheet margin. To achieve these objectives, this research will determine the timing of past extents of Jakobshavn Isbræ using beryllium-isotope exposure dating of ice-sculpted bedrock surfaces and boulders preserved on the landscape. This study will also utilize 3D mapping techniques to reconstruct ice sheet geometry that will assist in determining the influence of the underlying topography on ice sheet fluctuations. The broader impacts of this research include pioneering the detailed reconstruction of short-term paleo-fluctuations of a major ice stream in Greenland, assessing the sensitivity of Jakobshavn Isbræ to past abrupt climate events, and assessing the balance between climate and ice dynamic controls of Jakobshavn Isbræ behavior during past abrupt and short-lived climate perturbations. The methods used here will have practical applications for reconstructing paleo-ice margin changes of other large Greenland ice streams. This knowledge will result in the development of models that will improve the ability to predict changes in ice sheets and any resulting changes in sea-level.